The invention relates to a container for storing and transporting a liquefied gas, which container has a liquid space and a gas space which during operation are at a lower temperature level. A container of this type is described, for example, in a book by R. B. Scott, "Cryogenic Engineering" (D. Van Nostrand Company, Inc. 1959), page 226, wherein the vapor space of a transport dewar for liquid hydrogen accommodates a cooling coil through which cooled helium flows. The cooling coil ensures, by recondensation of hydrogen which may be evaporated owing to heat leak into the liquid, that the pressure in the dewar does not exceed a given value.
Such a construction has disadvantages. The use of the helium refrigerator renders the system complicated and expensive, and the vehicle carrying the dewar must be unnecessarily large to accommodate the refrigerator also. The latter condition results in increased cost of transportation.
Owing to the stringent safety regulations which generally must be observed when transporting a liquefied gas, such as liquid hydrogen, the thermal insulation and the further construction of transport dewars, transport tanks and the like have to satisfy exacting requirements. For example, in practice the condition must be satisfied that no venting of hydrogen vapor produced by heat leak into the liquid is necessary for 110 hours after the tank has been filled (see for example the paper: "The safe distribution and handling of hydrogen for commercial application," Paper No. 729,209, seventh Intersociety Energy Conversion Engineering Conference, San Diego, September 1972). This ensures that during transport no danger of explosion due to venting (hydrogen together with the oxygen of the air may form the readily exploding oxyhydrogen) can arise. However, the use of high-quality vacuum insulation is inevitable.
It is an object of the present invention to provide a transport dewar in which the abovementioned disadvantages are avoided.